CHEMISTRY COMMUNITY

Tasnia Haider 1E

There will be some questions on the functional groups which he introduced in class on Monday, so be able to recognize them if they are in line structures.

Tasnia Haider 1E

You want E to be positive because the reaction has to be spontaneous which only happens in galvanic cells. So, I believe that you have to flip the oxidation side if you are using that method of calculating E.

Tasnia Haider 1E

If it is a sealed container, the final volume is always constant. It seems like volume is changing because there is a divider, but overall volume is not changing.

Tasnia Haider 1E

I'm pretty sure you need to know all the enthalpies, but they should be on the equations sheet.

Tasnia Haider 1E

Hi, I have the other professor for a Tuesday lab from 11 am to 1:50 pm. If you would like this, let me know!

Tasnia Haider 1E

A gas phase has a higher level of entropy because there are more arrangements for the molecules. On the other hand, for liquids, entropy is lower because the liquid cannot have more arrangements.

Tasnia Haider 1E

At boiling point, the change in temperature is zero so change in enthalpy is also zero (infer that pressure is constant so W=0). Since change in enthalpy is zero, we also want change in entropy to be zero. This happens when W=0.

Tasnia Haider 1E

The slow step and the rate law should be the same in terms of reactants. The rate law should match the slow step’s reactants.

Tasnia Haider 1E

Also one the equation sheet, it won’t tell you what orde the derivations or integrations are so make sure to know which one is first, second, and zero orders.

Tasnia Haider 1E

When a product/reactant has a zero order, does that mean it’s concentration is independent of the rate?

Tasnia Haider 1E

In this question, Zinc has a more negative standard potential than Chromium, but the answer key shows that chromium is the stronger reducing agent. Why is that?

Tasnia Haider 1E

You use a comma when the ions or compounds are in the same state on the same side, and use a single line when they have different states.

Tasnia Haider 1E

For 14.13c why is the Cl- put before the Cl2 when they are the ones being reduced. Shouldn't Cl be put in front of the Cl- or does the phase matter?

Tasnia Haider 1E

I don't think it will because the half reactions need to be cancelled out. In the half reactions the H+ should be included and full compounds/ions.

Tasnia Haider 1E

Yes, for basic solutions, you add OH-.

Tasnia Haider 1E

To see which compounds are reduced or oxidized, you have to look at the oxidation states. Br is going from an oxidation state of 1- to 5+ which shows that it's being oxidized.

Tasnia Haider 1E

It should be under administrative questions, and will be labeled as Winter 2018 Practice Midterm.

Tasnia Haider 1E

In 9.47, the question asks about an isothermal, irreversible, free expansion. How do we know that the change in internal energy is zero from this phrase? Since internal energy is zero, that means q is also zero.

Tasnia Haider 1E

K is supposed to symbolize when the reaction is at equilibrium. The reactant quotient is when the reaction is not at equilibrium. When Q>K, that means there is too much product which means the reverse reaction is favored. When Q<K, that means there is too much reactant which means the forward reacti...

Tasnia Haider 1E

G is defined as the maximum non-expansion work under constant temperature and pressure. If work done by the system is negative, DeltaG < w, since G = H-TS = U+PV-TS.
Then DeltaG is the maximum work that may be done.

Tasnia Haider 1E

For the example shown in class today, why does deltaG have to be zero to find the minimum temperature?

Tasnia Haider 1E

Will we need to know how to derive the integral for the test/ midterm coming up?

Tasnia Haider 1E

in addition to what others said, bond enthalpies for diatomic molecules are the only exact calculations. Every other bond enthalpy is an average.

Tasnia Haider 1E

The third law of thermodynamics states that for a perfect crystal at absolute zero, the entropy is also zero.

Tasnia Haider 1E

Why does a reversible expansion do more work than an irreversible expansion?

Tasnia Haider 1E

Different phases need more energy to convert the substance into another state, so some need more energy which is what the heat capacity states.

Tasnia Haider 1E

This problem is just allowing you to see how benzene'S resonance allows it to have a lower molar energy than the different resonance structures that we can draw it of the c-c and c=c bonds. The kekule structure is the ones that we've drawn out with the 3 single and 3 double carbon bonds, while reson...

Tasnia Haider 1E

What is the difference between extensive and intensive properties? In the notes, it states that heat capacity is an extensive property while specific heat capacity is an intensive property.

Tasnia Haider 1E

Heat is not an internal property of the system. It depends on the path taken to go from point A to point B which is why it's not a state function.

Tasnia Haider 1E

It depends on how much material we cover before the Tuesday when the tests start in discussions. Usually it's material up to Friday before the test.

Tasnia Haider 1E

What is the difference between a delta H with a subscript of c and a delta H with a subscript of h? The delta h had a subscript of c in the homework problem in 8.57?

Tasnia Haider 1E

Hi,
Can you post the answers for the past two review worksheets for Week 7 and Week 9?

Tasnia Haider 1E

You can also count the number of electrons each compound or ion has. PF5 would have 40 electrons and F- would have 8 electrons. If PF6 didn't have a charge it would only have 47 electrons, but the structure should have the same number of electrons as its reactants, so it would need an extra electron...

Tasnia Haider 1E

When we calculate the pH for weak acids, and the change in concentration is extremely small because kA is extremely small, do we automatically assume the change in concentration for the initial concentration is negligible like how we did the example in lecture? Do we always have to check using the 5...

Tasnia Haider 1E

Do we have to memorize the list of weak acids and bases, and strong acids and bases for the final?

Tasnia Haider 1E

To find the coordination number, only look at the elements within the brackets and the number of ligands attached to the transition metal. Anything outside the brackets should not be counted.

Tasnia Haider 1E

When figuring out the order of coordination compounds, how do you know to put OH2 or H2O as the structure within the compound? It has them both ways in the solutions manual.

Tasnia Haider 1E

When figuring out the elements of a compound, does it matter in which way compounds are ordered in the coordination compound? For example in 17.31b, the compound is pentaamine sulfatocobalt(III) chloride, and the sulfate is mentioned second but is connected to the cobalt in the answer, [Co(SO4)(NH3)...

Tasnia Haider 1E

Are we going to have to show how we came up with the hybridized orbital on the test like how he did in class?

Tasnia Haider 1E

I don't think you need to unless he specifically asks for it. Otherwise, you can just normally do a Lewis structure.

Tasnia Haider 1E

What type of ionization energy and electron affinity doe noble gases have?

Tasnia Haider 1E

Yes, since the lowest energy structure means that the structure is the most stable for the compound or element.

Tasnia Haider 1E

Since Chlorine is in the n=3 shell, that means it can gain more electrons to put into a 3d shell, if necessary.

Tasnia Haider 1E

In all of the Lewis structures, the highest ionization energy atoms are the central atoms, even though we learned that the central atom should have the lowest ionization energy. Why is it like that? Is it only to show the resonance structures?

Tasnia Haider 1E

I think it means when an electron has gone through a full wave cycle that it means that it goes through a node.

Tasnia Haider 1E

The only exceptions we are required to know are Chromium and Copper.

Tasnia Haider 1E

Do all half-filled subshelled atoms always have a higher electron affinity than the atom right next to them because they are more stable? For example, carbon has a higher electron affinity than nitrogen. Does this also correspond with phosphorus and sulfur?

Tasnia Haider 1E

I think if you do the homework for chapter 2, the questions will be a little similar to what can be on his test.

Tasnia Haider 1E

Velocity should be in its SI units unless state otherwise on a test.

Tasnia Haider 1E

When finding the velocity of an electron, which formula should you use, E=pc or E=.5mv^2? Does it depend on if the electron is being described as a particle or a wavelength?

Tasnia Haider 1E

As the electron returns to a ground state, it's point of reference was at the highest energy level who's energy was zero. Since the electron is returning to a lower energy level, it is emitting energy and would have to be a negative number because of the reference point's energy which is zero.

Tasnia Haider 1E

Will we get this conversion, if needed, on the sheet of paper for the quiz, or do we have to memorize this?

Tasnia Haider 1E

Since the electron is returning to the ground state, it is emitting energy, which would be a negative number. However, this number is used to find wavelengths, and the calculation can't have a negative energy because then it would result in a negative wavelength, which isn't possible. The energy is ...

Tasnia Haider 1E

Quick question about these net ionic equation thing. Do we need to write the charges for everything or is that just a little extra thing that the solutions manual does? Like Cu2+ (aq) + 2OH-(aq) ... Also in regular reactions/equations when would we need to write the charges if ever? Also in a react...

Tasnia Haider 1E

When writing an empirical or molecular formula, how do you know in what order to write the elements? For example, how would you know to write Na3AlF6 rather than AlNa3F6 or Na3F6Al? When writing the molecular or empirical formula the order usually is the elements C followed by H, and then it always...

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